In the case of most processes taking place in the field of semiconductor production technology, the knowledge of the locus-dependent pressure and concentration characteristics of the gases, vapors and plasmas or of the process particles in general is of decisive importance as far as process monitoring and process control are concerned. A point of special interest in case of these processes is the homogeneity of the particle concentration in the process atmosphere above the semiconductor structure to be produced.
It is known that the pressure values occurring within the process chamber during a semiconductor-structure coating process can be monitored by means of pressure gauges, the following pressure gauges being used depending on the pressure to be monitored or measured: heat-conduction vacuum gauges for the fine vacuum region; cold-cathode vacuum gauges for high vacuum up to and into ultrahigh vacuum region; hot-cathode ionization vacuum gauges for the fine vacuum region up to the extreme ultrahigh vacuum region as well as quadruple mass spectrometers. Such pressure gauges cannot be used for a two-dimensional detection of concentration and/or pressure distributions of process particles. Nor is it possible to detect by means of such pressure gauges the concentration of the particles participating in the coating process itself, since the particles to be measured are withdrawn from the process by the known pressure gauges described above, and which suck in the particles.
From the field of flame diagnosis, a fluorescence measuring method is known, in the case of which a high-power dye laser light source is used for exciting the flame gases to emit fluorescent radiation. On the basis of the fluorescent radiation emitted, it is then possible to carry out a two-dimensional pressure detection within the flame. The sensitivity of this fluorescent measuring method known from the field of flame diagnosis is several orders of magnitude lower than the sensitivity required for control and measuring methods in the field of semiconductor production. Furthermore, the high-powered dye laser light sources which are required for flame diagnosis and which are sold at a price of approximately $200,000 per unit are too uneconomic for most cases of use outside purely basic research.
European Patent EP-A2-0070523 discloses a control and measuring European unit for use in the field of semiconductor production for detecting the concentration or the pressure of process particles at a location examined within the process chamber, within which a vacuum can be created, comprising a light beam source used for producing a light beam within the process chamber, the light beam penetrating an area of the process chamber which is to be examined and the wavelength of the light emitted by the light beam source being so short that the process particles have imparted thereto an excitation energy which suffices for fluorescent radiation, a pick-up device in the form of a detector, which is arranged such that its detection area is disposed at right angles to the light beam and the spectral sensitivity of which is chosen such that, in the spectral region of the fluorescent radiation of the process particles, said spectral sensitivity has a quantum efficiency which suffices for detecting the fluorescent radiation, and an integrator, which is connected to the detector and which is used for determining concentrations or pressures of the process particles at the location examined. However, the European reference does not disclose any information with regard to the concept of fanning the light so as to produce a substantially parallel light fan within the process chamber, nor does it disclose any information with regard to the use of a camera for planar detection of the fluorescent radiation within the process chamber for producing thus a two-dimensional image of the concentration distribution or of the pressure distribution of process particles within the process chamber.
In the case of the subject matter of European application EP-A2-0070523, it is, additionally, necessary to use high-powered, expensive Excimer laser units instead of comparatively low-powered laser light source which is used in the present invention. EP-A2-0070523 especially fails to refer in any way to the importance of the low pressure within the process chamber with regard to the use of low powered laser light sources or other light sources. For the purpose of full disclosure of the technological background of the present invention, reference is made to the following publications: DE-Al-3901017, GB-A-2104650; GB-A-2189881 and US-A-4394237.
The present invention solves the problem of creating a semiconductor production control and/or measuring unit for a two-dimensional detection and/or control of concentration and/or pressure distributions of process particles within a semiconductor production device.
The present invention is a semiconductor production control and/or measuring unit for a two-dimensional detection and/or control of concentration and/or pressure distributions of process particles within a process chamber, which forms part of a semiconductor production device and in the interior of which a vacuum can be generated with the aid of a vacuum pump means, the control and/or measuring unit comprising the following features:
a light fan source used for producing a substantially parallel light fan within the process chamber, the light fan penetrating the area of the process chamber which is to be examined with regard to concentration distribution and/or pressure distribution and the wavelength of the light fan source being so short that the process particles have imparted thereto an excitation energy which suffices for fluorescent radiation;
a camera which is arranged such that its camera direction is disposed at an angle with respect of the light fan and that it covers the area to be examined, the spectral sensitivity of the camera being selected such that, in the spectral region of the fluorescent radiation of the process particles, the camera has a quantum efficiency which suffices for detecting fluorescent radiation; and
a processing device, which is connected to the camera and which determines the two-dimensional concentration and/or pressure distribution of the process particles on the basis of the image signals received from the camera.
The present invention is based on the finding that, in spite of the high sensitivity required for the purpose of semiconductor production technology, it is possible to use the fluorescence measuring method, which, in the field of flame diagnosis, can only be realized with low sensitivity, since the problems of quenching and of Mie scattering by dust particles, which reduce the sensitivity of the fluorescence measuring method in the case of flame diagnosis, do not arise under the process conditions of semiconductor production technology. In view of the fact that the interfering effects of quenching and of Mie scattering do not occur, or occur only to an negligible extent, under the skeleton conditions of semiconductor technology, the light source used can be a light source of low power, e.g. a photoflash bulb. The price of such a light source is several orders of ten lower than the price of the dye laser light sources used in the field of flame diagnosis. It follows that the unit according to the present invention can also be realized at a reasonable price.